Optoelectronic Device and Method for Producing Same

ABSTRACT

A method for producing an optoelectronic component is disclosed. A first layer which has a dielectric to the surface of a semiconductor crystal. A photoresist layer is applied and structured on the first layer. The photoresist layer is structured in such a way that the photoresist layer has an opening, The first layer is partially separated in order to expose a lateral region of the surface. A contact area having a first metal is applied in the lateral region of the surface. The photoresist layer is removed. A second layer, which comprises an optically transparent, electrically conductive material, and a third layer, which comprises a second metal, are applied.

This patent application is a national phase filing under section 371 ofPCT/EP2014/058357, filed Apr. 24, 2014, which claims the priority ofGerman patent application 10 2013 104 953.2, filed May 14, 2013, each ofwhich is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a method for producing anoptoelectronic device and to an optoelectronic device.

BACKGROUND

In optoelectronic devices with semiconductor crystals, it is necessarythat contact areas for electrical contacting be reproducibly providedwith an optimum contact size. For example, it is necessary inlight-emitting diode devices reproducibly to produce optimallydimensioned contact areas in order to achieve low forward voltages andhigh light yields.

A prior art method is known for producing light-emitting diode chips(LED chips) using thin-film technology in which, in a first lithographicmethod step, a contact area of metal is provided. In a second methodstep, a layer of a mirror dielectric which covers the contact area isapplied. The minor dielectric is then opened up in the region of thecontact area by means of a photolithographic method. A mirror metalwhich simultaneously provides electrical contacting for the contact areais then deposited. As a result of adjustment tolerances during thelithographic process steps, this method gives rise to a scatter of theeffective size of the contact area.

SUMMARY

Embodiments of the present invention provide a method for producing anoptoelectronic device. Further embodiments of the present inventionprovide an optoelectronic device.

A method for producing an optoelectronic device comprises steps ofproviding a semiconductor crystal which has a surface, of applying afirst layer which comprises a dielectric onto the surface, of applyingand patterning a photoresist layer on the first layer, wherein thephotoresist layer is patterned in such a manner that it comprises anopening, of partially dissolving away the first layer in order touncover a lateral region of the surface, of applying a contact areawhich comprises a first metal in the lateral region of the surface, ofremoving the photoresist layer, of applying a second layer whichcomprises an optically transparent, electrically conductive material,and of applying a third layer which comprises a second metal. Thismethod advantageously produces an optoelectronic device with asemiconductor crystal with a contact area, the size of which may bedefined by the size of the opening in the photoresist layer. Thisadvantageously makes it possible to define the size of the contact areahighly accurately and reproducibly. The entire size of the contact areaadvantageously serves for electrically contacting the semiconductorcrystal, whereby it is not necessary to make the contact area largerthan necessary in order to compensate a tolerance. As a result, it isadvantageously possible to minimise absorption of light generated in thesemiconductor crystal at the contact area, for which reason theoptoelectronic device produced by the method may have a higher lightyield. A further advantage of the method is that it requires just onephotolithographic process step, whereby the method may be carried outinexpensively.

In one embodiment of the method, the photoresist layer comprises apositive resist. The photoresist layer can then advantageously bepatterned by exposing only the region in which the opening is to beproduced.

In one embodiment of the method, the first layer is partially dissolvedaway by wet chemical etching. As a result, the method may advantageouslybe carried out simply and inexpensively.

In one embodiment of the method, the photoresist layer is partiallyunderetched while the first layer is being dissolved away. Partialunderetching advantageously ensures that the size of the resultantcontact area highly accurately matches the size of the opening in thepatterned photoresist layer.

An optoelectronic device comprises a semiconductor crystal with asurface which comprises a first lateral region, a second lateral regionand a third lateral region. In the first lateral region, a contact areais here arranged on the surface which comprises a first metal. In thethird lateral region, a first layer is arranged on the surface whichcomprises a dielectric. A second layer which comprises an opticallytransparent, electrically conductive material is arranged on the contactarea, the first layer and the second lateral region of the surface. Athird layer which comprises a second metal is here arranged on thesecond layer. In this optoelectronic device, the entire area of thecontact area advantageously serves for electrically contacting thesemiconductor crystal, whereby the contact area may be formed with smalldimensions. Light absorption at the contact area is advantageouslyreduced as a consequence, whereby a light yield of the optoelectronicdevice may be improved. One advantage is that light absorption in thesecond lateral region is substantially lower than light absorption inthe first lateral region at the contact area. As a result, both aforward voltage of the optoelectronic device and a light yield of theoptoelectronic device are virtually independent of the size of thesecond lateral region. This enables simple and inexpensive production ofthe optoelectronic device. A further advantage may be that the secondlayer serves as a bonding agent between the first layer and the thirdlayer.

In one embodiment of the optoelectronic device, a specific contactresistance between the second layer and the semiconductor crystal is atleast one order of magnitude higher than a specific contact resistancebetween the contact area and the semiconductor crystal. As a result, thesecond layer advantageously electrically contacts the semiconductorcrystal substantially less than the contact area. The consequence ofthis is that a forward voltage of the optoelectronic device isdetermined only by the contact area. This advantageously gives rise tohigh reproducibility of the forward voltage.

In one embodiment of the optoelectronic device, the second lateralregion at least in places annularly surrounds the first lateral region.As a result, the second lateral region advantageously forms a safety gapbetween the contact area and the first layer of the optoelectronicdevice. This enables production of the contact area with a reproduciblesize.

In one embodiment of the optoelectronic device, the third lateral regionat least in places annularly surrounds the second lateral region. As aresult, the contact area is advantageously arranged in an opening of thefirst layer arranged and is spaced from the first layer, whereby thecontact area can be produced with a readily reproducible size.

In one embodiment of the optoelectronic device, the opticallytransparent, electrically conductive material is a transparent,electrically conductive oxide. Transparent, electrically conductiveoxides advantageously have a low optical absorbency and electricallycontact semiconductor crystals with a high contact resistance.Transparent, electrically conductive oxides are here advantageouslynevertheless suitable for electrically contacting the contact area.

In one embodiment of the optoelectronic device, the first metal and/orthe second metal is gold or silver. These metals advantageously havefavourable optical and electrical properties.

In one embodiment of the optoelectronic device, the dielectric comprisesSiO₂. As a result, reflectivity of the third layer is advantageouslyimproved.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-described characteristics, features and advantages of thisinvention and the manner in which these are achieved will become clearerand more distinctly comprehensible from the following description of theexemplary embodiments, which are explained in greater detail inconnection with the drawings, in which in each case in a schematicrepresentation

FIG. 1 shows a semiconductor crystal for producing an optoelectronicdevice;

FIG. 2 shows the semiconductor crystal with an applied first layer;

FIG. 3 shows the first layer with a patterned photoresist layer arrangedthereon;

FIG. 4 shows the first layer after the first layer has been partiallydissolved away;

FIG. 5 shows the semiconductor crystal, the first layer and thephotoresist layer after application of a metal layer;

FIG. 6 shows the semiconductor crystal, the first layer and a contactarea after detachment of the photoresist layer;

FIG. 7 shows the unfinished optoelectronic device after application of asecond layer;

FIG. 8 shows the unfinished optoelectronic device after application of athird layer; and

FIG. 9 shows the optoelectronic device after application of a fourthlayer.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 shows a highly schematic sectional representation of asemiconductor crystal 100. The semiconductor crystal 100 may, forexample, be produced by epitaxial growth. The semiconductor crystal 100has a surface 110.

The semiconductor crystal 100 is provided for producing anoptoelectronic device, for which purpose further processing steps, whichare explained below, are required. The optoelectronic device may, forexample, be a light-emitting diode device.

FIG. 2 shows a schematic sectional representation of the semiconductorcrystal 100 in a processing state chronologically subsequent to therepresentation of FIG. 1. A two-dimensional first layer 200 has beenarranged on the surface 110 of the semiconductor crystal 100. The firstlayer 200 comprises a dielectric which serves as minor dielectric. Thefirst layer 200 may, for example, comprise silicon dioxide (SiO₂). Thefirst layer 200 may, for example, have been applied by chemical vapourdeposition onto the surface 110 of the semiconductor crystal 100.

FIG. 3 shows a schematic sectional representation of the semiconductorcrystal 100 in a processing state chronologically subsequent to therepresentation of FIG. 2. A photoresist layer 300 has been arranged onthe side of the first layer 200 remote from the semiconductor crystal100. The photoresist layer 300 has moreover been patterned in order toproduce an opening 310 in the photoresist layer 300, through which thefirst layer 200 is accessible. The opening 310 in the photoresist layer300 preferably has a circular disc-shaped cross-sectional area. Theopening 310 may, however, also have another cross-sectional shape. Theopening 310 has an opening diameter 311 in the lateral direction.

The photoresist layer 300 may comprise a positive resist. In this case,the photoresist of the photoresist layer 300 was exposed in the regionof the opening 310. The exposed parts of the photoresist layer 300 werethen dissolved away.

FIG. 4 shows a schematic sectional representation of the semiconductorcrystal 100 in a processing state chronologically subsequent to therepresentation of FIG. 3. The first layer 200 arranged on the surface110 of the semiconductor crystal 100 has been partially removed. Removalof the part of the first layer 200 has preferably been performed by wetchemical etching. The wet chemical etchant has here attacked the firstlayer 200 through the opening 310 in the photoresist layer 300.

As a result of the first layer 200 having been partially dissolved away,an opening 210 accessible through the opening 310 in the photoresistlayer 300 has arisen in the first layer 200, which opening 210 uncoversthe surface 110 of the semiconductor crystal 100 in an uncovered lateralregion 120. In a covered region 111, the surface 110 of thesemiconductor crystal 100 is still covered by the first layer 200 evenafter part of the first layer 200 has been dissolved away. The lateralregion 120 of the surface 110 of the semiconductor crystal 100 uncoveredby the opening 210 in the first layer 200 has an uncovered diameter 123.The uncovered diameter 123 is preferably larger than the openingdiameter 311 of the opening 310 in the photoresist layer 300. In aprojection perpendicular to the surface 110 of the semiconductor crystal100, the centre points of the opening 310 in the photoresist layer 300and the centre point of the uncovered lateral region 120 of the surface110 of the semiconductor crystal 100 with the uncovered diameter 123preferably lie approximately on one another.

Since the diameter of the opening 210 in the first layer 200 is largerin the lateral direction than the opening diameter 311 of the opening310 in the photoresist layer 300, an underetch 220 has been formed underthe photoresist layer 300. The photoresist layer 300 has thus beenpartially underetched while the first layer 200 was being partiallydissolved away.

FIG. 5 shows a schematic sectional representation of the semiconductorcrystal 100 in a processing state chronologically subsequent to therepresentation of FIG. 4. A metal layer 400 has been deposited from thephotoresist layer 300 side. The metal layer 400 has settled on the sideof the photoresist layer 300 remote from the first layer 200. Materialof the metal layer 400 has moreover passed through the opening 310 inthe photoresist layer 300 to reach the uncovered lateral region 120 ofthe surface 110 of semiconductor crystal 100 and has there formed acontact area 410. The contact area 410 covers the uncovered lateralregion 120 of the surface 110 of the semiconductor crystal 100 in acontact region 121. The contact region 121 is approximately centrallyarranged in the uncovered lateral region 120 of the surface 110 of thesemiconductor crystal 100 and is bordered to the outside by a toleranceregion 122, which is annular or at least in places annular, of theuncovered lateral region 120. The tolerance region 122 of the uncoveredlateral region 120 is surrounded to the outside annularly or at least inplaces annularly by the covered region 111 of the surface 110 of thesemiconductor crystal 100.

The contact area 410 has a contact diameter 124 in the lateral directionwhich is smaller than the uncovered diameter 123. The contact diameter124 of the contact area 410 approximately matches that of the openingdiameter 311 of the opening 310 in the photoresist layer 300. Theopening diameter 311 of the opening 310 in the photoresist layer 300thus defines the contact diameter 124 of the contact area 410.

The metal layer 400 comprises an electrically conductive material. Themetal layer 400 may, for example, comprise gold or silver. The metallayer 400 may also comprise a bonding agent such as platinum, titaniumor chromium which is applied prior to application of the remainder ofthe metal layer 400 in order to improve adhesion of the metal layer 400.

The contact area 410 formed from the metal layer 400 is in goodelectrical contact with the semiconductor crystal 100. A specificcontact resistance between the contact area 410 and the semiconductorcrystal 100 is preferably low.

The underetch 220 of the photoresist layer 300 ensures that the part ofthe metal layer 400 arranged on the photoresist layer 300 is notconnected to the part of the metal layer 400 which forms the contactarea 410. This allows the part of the metal layer 400 arranged on thephotoresist layer 300 to be lifted off using a lift-off method.

FIG. 6 shows a schematic sectional representation of the semiconductorcrystal 100 in a processing state chronologically subsequent to therepresentation of FIG. 5. The photoresist layer 300 has been removedtogether with the part of the metal layer 400 arranged on thephotoresist layer 300. On the surface 110 of the semiconductor crystal100, there thus remain the first layer 200 with the opening 210 and thecontact area 410 arranged in the contact region 121 of the uncoveredlateral region 120 of the surface 110 of the semiconductor crystal 100.

FIG. 7 shows a schematic sectional representation of the semiconductorcrystal 100 in a processing state chronologically subsequent to therepresentation of FIG. 6. A second layer 500 has been arranged on thesurface 110 of the semiconductor crystal 100, the contact area 410 andthe first layer 200. The second layer 500 covers the side of the firstlayer 200 remote from the semiconductor crystal 100, the toleranceregion 122 of the uncovered lateral region 120 of the surface 110 of thesemiconductor crystal 100, the contact area 410 and preferably also thewall of the opening 210 in the first layer 200.

The second layer 500 comprises a transparent, electrically conductivematerial. The second layer 500 may, for example, comprise a transparent,electrically conductive oxide such as for instance doped zinc oxide,indium-zinc oxide or indium-tin oxide. The transparent, conductivematerial is transparent in an electromagnetic wavelength range whichcomprises a wavelength of the electromagnetic radiation emitted by theoptoelectronic device which is produced from the semiconductor crystal100. The transparent, conductive material may, for example, have anabsorption coefficient of 1000 per centimetre.

The material of the second layer 500 scarcely electrically contacts thesemiconductor crystal 100 in the tolerance region 122 of the surface 110of the semiconductor crystal 100. There is preferably a very highspecific contact resistance between the second layer 500 and thesemiconductor crystal 100. The specific contact resistance between thesecond layer 500 and the semiconductor crystal 100 is at least one orderof magnitude higher than the specific contact resistance between thecontact area 410 and the semiconductor crystal 100. There is anelectrically highly conductive connection between the contact area 410and the second layer 500.

FIG. 8 shows a schematic representation of the semiconductor crystal 100in a processing state chronologically subsequent to the representationof FIG. 7. A third layer 600 has been applied onto the second layer 500.The third layer 600 serves as mirror layer and preferably comprises ametal. The third layer 600 may, for example, comprise gold or silver.The second layer 500 arranged between the first layer 200 and the thirdlayer 600 may serve as bonding agent for the third layer 600.

The third layer 600 is electrically conductively connected via thesecond layer 500 to the contact area 410. In an optoelectronic deviceproduced from the semiconductor crystal 100, the third layer 600 mayserve to guide an electrical contact to the contact area 410 to theoutside.

FIG. 9 shows a schematic sectional representation of the semiconductorcrystal 100 in a processing state chronologically subsequent to therepresentation of FIG. 8. In the processing state shown in FIG. 9, thesemiconductor crystal 100 is part of a largely finished optoelectronicdevice 10. The optoelectronic device 10 may, for example, be alight-emitting diode device. The semiconductor crystal 100 is then anLED chip.

A fourth layer 700 has been applied onto the third layer 600. The fourthlayer 700 may serve as bonding layer to a carrier or substrate of theoptoelectronic device 10.

The optoelectronic device 10 may be electrically contacted via the thirdlayer 600 and the contact area 410, as well as the interposed secondlayer 500. The contact area 410 has the contact diameter 124 which isdefined by the opening diameter 311 of the opening 310 of thephotoresist layer 300, which opening diameter may be reproduciblyestablished with elevated accuracy. The method described with referenceto FIGS. 1 to 9 thus allows the contact diameter 124 of the contact area410 to be formed reproducibly with elevated accuracy. This results ingood reproducibility of a forward voltage of the optoelectronic device10. Since the second layer 500 is in practically no electrical contactwith the semiconductor crystal 100 in the tolerance region 122 of theuncovered lateral region 120 of the surface 110 of the semiconductorcrystal 100, the forward voltage is virtually unaffected by the size ofthe tolerance region 122. The uncovered diameter 123 of the lateralregion 120 which is uncovered during provision of the opening 210 in thefirst layer 200 thus has practically no effect at all on the forwardvoltage of the optoelectronic device 10.

When the optoelectronic device 10 is in operation, electromagneticradiation, for example, visible light, is generated in the semiconductorcrystal 100. Electromagnetic radiation which leaves the semiconductorcrystal 100 through the surface 110 is reflected back into thesemiconductor crystal 100 by the first layer 200 and the third layer 600in order to increase light yield from the optoelectronic device 10.

In the region of the contact area 410, electromagnetic radiationemerging from the semiconductor crystal 100 is at least in part absorbedby the first surface 110. Since almost no adjustment tolerances have tobe taken into account when forming the contact area 410, a comparativelysmall contact diameter 124 of the contact area 410 can be selected andtherefore the overall proportion of electromagnetic radiation absorbedat the contact area 410 is low.

Electromagnetic radiation emerging from the semiconductor crystal 100 inthe tolerance region 122 of the uncovered lateral region 120 of thesurface 110 is only absorbed to a substantially smaller extent than inthe region of the contact area 410. Electromagnetic radiation emergingfrom the semiconductor crystal 100 in the tolerance region 122 of theuncovered lateral region 120 of surface 110 is also substantiallyreflected on the third layer 600 back into the semiconductor crystal100. As a result, the achievable light yield of the optoelectronicdevice 10 is largely independent of the size of the tolerance region 122and thus also of the uncovered diameter 123 of the uncovered lateralregion 120.

The invention has been illustrated and described in greater detail withreference to the preferred exemplary embodiments. The invention isnevertheless not restricted to the disclosed examples. Rather, othervariations may be derived by a person skilled in the art without goingbeyond the scope of protection of the invention.

1-11. (canceled)
 12. A method for producing an optoelectronic device,the method comprising: providing a semiconductor crystal that has asurface; applying a first layer that comprises a dielectric onto thesurface; applying and patterning a photoresist layer on the first layer,wherein the photoresist layer is patterned in such a manner that itcomprises an opening; partially dissolving away the first layer in orderto uncover a lateral region of the surface; applying a contact area thatcomprises a first metal in the lateral region of the surface; removingthe photoresist layer; applying a second layer that comprises anoptically transparent, electrically conductive material; and applying athird layer that comprises a second metal.
 13. The method according toclaim 12, wherein the photoresist layer comprises a positive resist. 14.The method according to claim 12, wherein the first layer is partiallydissolved away by wet chemical etching.
 15. The method according toclaim 14, wherein the photoresist layer is partially underetched whilethe first layer is being dissolved away.
 16. The method according toclaim 12, wherein the size of the contact area highly accurately matchesthe size of the opening in the photoresist layer.
 17. The methodaccording to claim 12, wherein the uncovered lateral region of thesurface of the semiconductor crystal has a diameter, the diameter beinglarger than an opening diameter of the opening in the photoresist layer.18. The method according to claim 12, wherein a diameter of the openingin the first layer is larger than an opening diameter of the opening inthe photoresist layer.
 19. The method according to claim 12, wherein thephotoresist layer is partially underetched while the first layer isbeing dissolved away and wherein an underetch is formed under thephotoresist layer.
 20. An optoelectronic device comprising: asemiconductor crystal with a surface that comprises a first lateralregion, a second lateral region and a third lateral region, a contactarea arranged on the surface in the first lateral region, the contactarea comprising a first metal; a first layer that comprises a dielectricarranged on the surface in the third lateral region; a second layer thatcomprises an optically transparent, electrically conductive materialarranged on the contact area, the first layer and the second lateralregion of the surface; and a third layer that comprises a second metalarranged on the second layer.
 21. An optoelectronic device according toclaim 20, wherein a specific contact resistance between the second layerand the semiconductor crystal is at least one order of magnitude higherthan a specific contact resistance between the contact area and thesemiconductor crystal.
 22. An optoelectronic device according to claim20, wherein the second lateral region annularly surrounds the firstlateral region at least in places.
 23. An optoelectronic deviceaccording to claim 20, wherein the third lateral region at least inplaces annularly surrounds the second lateral region.
 24. Theoptoelectronic device according to claim 20, wherein the opticallytransparent, electrically conductive material is a transparent,electrically conductive oxide.
 25. The optoelectronic device accordingto claim 20, wherein at least one of the first metal and the secondmetal is gold or silver.
 26. The optoelectronic device according toclaim 20, wherein the dielectric comprises SiO₂.
 27. The optoelectronicdevice according to claim 20, wherein the third layer is electricallyconductively connected to the contact area via the second layer.
 28. Amethod for producing an optoelectronic device, the method comprising:providing a semiconductor crystal which has a surface; applying a firstlayer that comprises a dielectric onto the surface; applying andpatterning a photoresist layer on the first layer, wherein thephotoresist layer is patterned in such a manner that it comprises anopening; partially dissolving away the first layer in order to uncover afirst and a second lateral region of the surface such that the firstlayer is arranged on the surface in a third lateral region; applying acontact area that comprises a first metal in the lateral region of thesurface; removing the photoresist layer; applying a second layer on thecontact area, the first layer and the second lateral region of thesurface, the second layer comprising an optically transparent,electrically conductive material; and applying a third layer on thesecond layer, the third layer comprising a second metal, wherein aspecific contact resistance between the second layer and thesemiconductor crystal is at least one order of magnitude higher than aspecific contact resistance between the contact area and thesemiconductor crystal.